1. Technical Field
The present invention relates in general to an open cell composite structure and, in particular, to an improved system, method, and apparatus for an open cell, woven, and/or braided composite truss for forming a wet wing structure.
2. Description of the Related Art
Foam and honeycomb are often used as core materials for sandwich core composite load bearing structures. When used for aircraft wing box construction, sandwich core composite structures present manufacturing and weight advantages over traditional rib 10 and spar 12 wing box structures (FIG. 8). The low density of these structures permits extensive use where weight factors are critical, such as with air vehicle applications.
Properly configured rib and spar structures provide internal support for airplane wings. When these designs are used for fuel storage, a structure known as “wet wing” is formed. Wet wings typically comprise building an open structure formed from an upper and lower “skin” sealed to a rib and spar internal support structure to contain liquid fuel for use by the aircraft.
The design of wet wing structures prevents large shifts in the fuel during acceleration, deceleration, or other movement of the aircraft. However, manufacturing a rib and spar wing structure is a labor intensive process that also complicates the design of a wing. A core-stiffened skin sandwich composite wing structure can be easier to design and more efficient to manufacture.
FIGS. 1 and 2 show diagrams of various traditional wing box designs. FIG. 1 shows a rib and spar wing box design. The load bearing upper and lower skins 13, 15 are supported by an internal substructure comprised of ribs 17 and spars 19. This design provides volume for a wet wing. However, its design and manufacture are complicated by the many individual substructure elements along with the associated tooling and labor for assembly. FIG. 2 shows a sandwich composite wing box design that uses a honeycomb or foam core internal structure 23 to support its load bearing skins 25, 27. This design provides a manufacturing advantage over rib and spar wing box designs. However, it does not provide volume for fuel storage.
Unfortunately, neither foam nor honeycomb material are appropriate as a core material if the structure is intended to be used for fuel storage. Even open cell foam or perforated honeycomb is insufficient due to extremely high surface areas that trap or retain fuel rather than making it available to the aircraft. Honeycomb material is further handicapped because its mechanical properties are anisotropic. Thus, an improved wing box design that preferably incorporates an isotropic core material suitable for use in a wet wing design would be desirable.